1. Field of the Invention
This invention relates to a modified polytetrafluoroethylene (hereunder abbreviated as PTFE) that is improved in radiation resistance (as evidenced by reduction in the radiation-induced deterioration of breaking extension and breaking strength) and which has rubber characteristics. The invention also relates to a process for producing such modified PTFE by applying an ionizing radiation to a starting PTFE.
2. Description of the Prior Art
PTFE is a plastic material having improved resistance to chemicals and heat and it has heretofore been used extensively as both industrial and consumer resins. Further, PTFE is a crystalline polymer; although PTFE is a resin that has a comparatively high hardness and low rubber characteristics, it will easily undergo plastic deformation at low temperatures such as room temperature. However, PTFE is very sensitive to radiations and its mechanical characteristics will deteriorate if the absorbed dose exceeds 1 kGy; hence, PTFE has been unsuitable for use in nuclear facilities and other environments of exposure to radiations. This is because molecular cleavage occurs preferentially in PTFE upon exposure to radiation, which contributes to accelerated progress of crystallization.
Currently available PTFEs are typical radiation-degradable plastics and to make them suitable for use not only in nuclear facilities and other environments of exposure to radiations but also in sealing and packing materials, it has been desired to impart radiation resistance (i.e., reduction in the radiation-induced deterioration of breaking extension and breaking strength), as well as low crystallinity and rubber characteristics.